1. Field of the Invention
The present invention relates to accelerometers. More particularly, the present invention relates to an accelerometer signal processor comprising variable oscillators and counters.
2. Description of the Prior Art
Accelerometers are employed in various applications to detect and compensate for disturbances, such as a shock or periodic vibration. An example is a disk drive which employs an accelerometer to detect disturbances affecting an actuator arm while attempting to maintain a head over a centerline of a track. The output of the accelerometer is used as a feed-forward compensation signal in a servo control system to effectively reject the disturbance.
Conventional accelerometers comprise a sensor for detecting accelerations, and signal processing circuitry for converting the sensor signals into acceleration signals representing a direction and magnitude of the detected accelerations. The acceleration signals are typically generated as digital signals for processing by other control circuitry, such as a servo controller in a disk drive. A conventional Analog-to-Digital converter (ADC) is typically employed to convert the analog sensor signals into digital sensor signals, and the digital sensor signals processed to generate the digital acceleration signals. However, a conventional ADC implemented with analog circuitry is relatively expensive due to its size and complexity.
There is, therefore, a need to reduce the cost of the signal processing circuitry used to convert the analog sensor signals of an accelerometer into digital acceleration signals representing a direction and magnitude of detected accelerations.
The present invention may be regarded as an accelerometer signal processor for use in processing sensor signals generated by an accelerometer. The accelerometer comprises a sensor for generating A, B, C and D sensor signals in response to a sensor excitation. The accelerometer signal processor comprises an A variable oscillator (VO) for generating an A oscillating signal in response to the A sensor signal, a B VO for generating a B oscillating signal in response to the B sensor signal, a C VO for generating a C oscillating signal in response to the C sensor signal, and a D VO for generating a D oscillating signal in response to the D sensor signal. A first axis counter comprising an up count input responsive to the A oscillating signal and a down count input responsive to the D oscillating signal generates on output signal indicative of an acceleration along a first axis. A second axis counter comprising an up count input responsive to the B oscillating signal and a down count input responsive to the C oscillating signal generates on output signal indicative of an acceleration along a second axis. A rotation counter comprising an up count input responsive to the A and D oscillating signals and a down count input responsive to the B and C oscillating signals generates an output signal indicative of a rotational acceleration.
In one embodiment, the accelerometer signal processor comprises a first summing circuit for summing frequencies of the A and D oscillating signals to generate an output signal applied to the up count input of the rotation counter, and a second summing circuit for summing frequencies of the B and C oscillating signals to generate an output signal applied to the down count input of the rotation counter.
In one embodiment, the sensor comprises an optical sensor and the sensor excitation comprises light. In one embodiment, the accelerometer comprises an AGC counter responsive to the A, B, C and D oscillating signals and a reference oscillating signal. The AGC counter for generating an AGC signal for controlling the sensor excitation.
The present invention may also be regarded as a method of processing sensor signals generated by an accelerometer comprising a sensor for generating A, B, C and D sensor signals in response to a sensor excitation signal. The method comprises the steps of generating an A oscillating signal in response to the A sensor signal, generating a B oscillating signal in response to the B sensor signal, generating a C oscillating signal in response to the C sensor signal, and generating a D oscillating signal in response to the D sensor signal. The method further comprises the step of up-counting a first-axis counter in response to the A oscillating signal and down-counting the first-axis counter in response to the D oscillating signal, the first axis counter for generating an output signal indicative of a first linear acceleration. The method further comprises the step of up-counting a second axis counter in response to the B oscillating signal and down-counting the second axis counter in response to the C oscillating signal, the second axis counter for generating on output signal indicative of a second linear acceleration. The method further comprises the step of up-counting a rotation counter in response to the A and D oscillating signals and down-counting the rotational counter in response to the B and C oscillating signals, the rotation counter for generating an output signal indicative of the rotational acceleration.